Blocking oscillator system



A. K. DRAKE ET AL BLOCKING OSCILLATOR SYSTEM Filed Aug. 21, 1958 \WNEW RM r mam s m? WW M 1/.V 0 KM w w A 2 r m fin V. B

March 27, 1962 United States Patent Ofiice 3,027,517 Patented Mar. 27,1962 3,027,517 BLOCKING OSCHLLATOR SYSTEM Arthur K. Drake, Braintree,and Douglas 0. Cochrane,

Dorchester, Mass., assignors to Edgerton Germeshausen and Grier, Inc.,Boston, Mass, a corporation of Massachusetts Filed Aug. 21, 1958, Ser.No. 756,379 6 Claims. (Cl. 328242) The present invention relates toblocking oscillator systems and, more particularly, to those employingelectron tubes as the relay element of the oscillator.

Numerous types of blocking oscillators for generating electric impulseshave been proposed throughout the years, employing electron-tube relaysconnected with time-constant-controlled networks and an inputcircuit-tooutput circuit transformer, as described, for example, inUnited States Letters Patent No. 2,677,788, issued May 4, 1954, toKenneth J. Germeshausen. -It has been found that, for purposes laterexplained, the transformer, with its inherent restriction uponhigh-frequency response, can be eliminated and improved operation can beobtained if an electron tube embodying a secondary electron-emittingelectrode is employed in a novel oscillator circuit. An object of thepresent invention, therefore, is to provide a new and improved blockingoscillator system embodying such an electron tube having a secondaryelectron-emitting electrode.

A further object is to provide a new and improved oscillator that neednot employ a transformer.

Other and further objects will be explained hereinafter and will be moreparticularly pointed out in the appended claims.

In summary, the present invention relates to the employment of theabove-mentioned type of electron tube having an internal secondaryelectron-emitting electrode and provided with input and output circuits.A network, such as a capacitance-resistance circuit, is connected withthe input and output circuits for controlling the operation of theblocking-oscillator tube. Means is provided for biasing the secondaryelectron-emitting electrode to cause it to emit secondary electrons uponthe impingement thereupon of electrons in the tube during the operationof the same, and a further circuit connection is provided to thesecondary electron-emitting electrode for coupling therefrom an outputimpulse produced by the operation of the tube. Preferred circuit detailsare hereinafter set forth.

The invention will now be described in connection with the accompanyingdrawing, the single FIGURE of which is a schematic circuit illustratingthe invention in preferred form.

Referring to the drawing, the electron tube 1 is shown embodying acathode electrode 3 as a primary-emitting source of electrons, acontrol-grid electrode 5, a screengrid electrode 7, a groundedbeam-forming electrode 9, and an anode-electrode 11, together with asecondary electron-emitting dynode electrode 13 preferably disposed nearthe anode 11. The tube 1 may be of the type EFP60 and is connected intoa blocking-oscillator circuit, generally indicated by the numeral 2. Theanode 11 is connected through an anode load resistor 19 to the positiveterminal B-lof a source of anode potential, the negative B terminal ofwhich is preferably grounded, as shown, and is connected through acathode resistor 15 to the cathode electrode 3. The term ground, as usedherein, is intended to connote not only actual ealthing, but also anyreference potential, such as chassis potential and the like. Thescreen-grid electrode 7 is connected to a source of positive potentialB'-}- which may be of the same order of magnitude as the anode potentialB+, and is decoupled to ground through a capacitor 17.

Connected to the input circuit comprising the cathode 3 and controlelectrode 5 of the electron tube 1 is a source of impulses,schematically illustrated by the coaxial input terminals 4 and 6, thelatter of which is shown grounded. In the vent that the oscillator tube1 is to be externally triggered, the terminals 4 and 6 may be connectedto a pulse generator or other impulse source, no shown. It will beevident from the description hereinafter contained, however, that theoscillator may also, if desired, be freerunning, as described in thesaid Letters Patent. A diode 8 is shown connected from the inputterminal 4 to ground, in order to insure that only input signals of thedesired polarity are applied through the grid-resistor 10, to thecontrol-electrode 5. A shunt-connected input grid resistor 12 isconnected between the input terminal 4 and the input terminal 6, throughthe ground. The cathode 3 of the tube 1 may be positively biased byconnection through respective resistors R and 14 to a positive biasingpotential source Connected between the anode 11 and the cathode 3, isthe blocking oscillator network comprising one of a plurality ofcondensers C C C C C or C any one which may be selected by the rotationof a switch S, for a purpose later-described. In the drawing, the anode11 is shown connected by conductor 16 through the switch S to capacitorC and thence, by conductor 18, to the right-hand terminals of thebefore-mentioned resistor R and diode D The anode is also connect-ed tothe right hand terminals of resistor R and diode D through capacitor Cwhich serves as a by-pass for switch S. The resistance of resistor R is,of course, very large as compared to the almost resistance-freeconnection through diode D for signals of the proper polarity and,therefore, the feedback circuit for the blocking oscillator is from theanode 11 by way of the parallel paths comprising connector 16, switch S,the capacitor C to C selected by switch S and connector 13 on the onehand, and capacitor O; on the other, through diode D to the cathode 3. Asimilar feedback circuit could be employed between the dynode 13 and thecontrol grid 5. Diode D is connected in parallel with resistor R and issubject to a reverse bias substantially equal to the cathode bias oftube 1 across resistor R. The time duration of the blocking oscillatorpulse is determined by the level of the anode current in relation to thecapacity of the selected capacitance, C to C and C together with thecircuit parameters including the resistan-ces of R. 14. 15 and 19.

The tube 1 is preferably operated substantially Class A, being normallyconducting. All the voltages and currents are stabilized. The anodecurrent in this condition is approximately one milliampere or more. Thisis preferable in order to operate tube 1 at a high mutual conductancelevel and thereby utilize the increased amplification factor of tube 1.Capacitor C and one of the capacitors C to C as selected by switch S,are charged to a potential substantially equal to the difference betweenanode potential derived from B+ through resistor 19 and the potential atthe right hand terminal of diode D When a trigger pulse is fed tocontrol grid 5, tube 1 starts to amplify and the electrons emitted bythe cathode 3 are directed to secondary-olectron-emitting electrode 13.Upon the impingment of primary electrons, a greater number of secondaryelectrons are emitted which flow to anode 11. Tube 1 acts as anamplifier with a rapid increase in anode current and a correspondinglyrapid voltage drop across resistor 19 which together produce a negativepulse which is fed back to the right hand terminal of diode D where itnot only overcomes the reverse bias and passes through diode D therebymaking the cathode 3 more negative with respect to the grid 5, but alsoopposes the source of the cathode bias to decrease that bias,

thereby increasing the mutual conductance of the tube which in turnproduces an increase in anode current. Gnly an insignificant pant of thefeed-back pulse passes through resistor R because, as previouslymentioned, the resistance of R is very large in comparison with that ofdiode D When the reverse bias of diode D is overcome, diode D actssubstantially as a closed switch providing a direct connection for thefeed-back pulse from the anode 11 to the cathode 3, by-passing resistorR. The rapid potential drop at anode 11 causes a. rapid discharge, ordecrease in potential, of the aforementioned charge on the capacitors inthe feed-back circuit. The time-duration of the blocking oscillatorpulse is controlled by the time required for the capacitors to decreasein potential to the new potential level between the said points and bythe other circuit parameters previously mentioned. When the charge onthe said capacitors decreases to this level, there is no longer anegative pulse suflicient to overcome the reverse bias of diode D sothis reverse bias again takes control and the output pulse ends.Regeneration is thereafter prevented by the reverse bias across diode Duntil tube 1 is triggered anew and the entire process is repeated.

During the flow of electrons from the cathode 3 to the anode 11,electrons will strike the secondary electronemitting electrode 13. Theelectrode 13 is connected through'resistor 20 to a positive biaspotential source that renders the electrode 13 adaptable to emitsecondary electrons upon the impingement of primary electrons thereupon.The secondary electrons thus emitted from the secondaryelectron-emitting electrode 13 will then be directed to the adjacentanode 11. There will thus result at the secondary electrode 13 animpulse corresponding to the electron flow within the tube 1, which, inaccordance with the present invention, is coupled-out therefrom by thecoupling capacitor C to a pair of load circuits.

The first load circuit is shown fed from the capacitor C to a commonpoint P and then through a coupling capacitor C" and a resistor 22, to,for example, the com trol grid of a cathode-ray tube, not shown, as forthe purpose of intensifying the same or cutting the same off insynchronism with the pulses produced by the blocking oscillator tube 1.The second load circuit connected to the coupling capacitor C is thecathode follower stage 21, the control-grid electrode 23 of which isconnected to the point P through a resistor 45. The cathode 25 of thetube 21 is provided with a cathode load 27, the lower terminal of whichis grounded at D and the upper terminal of which connects through afurther coupling capacitor C' to a pair of output terminals 4', 6. Theoutputterminals 4', 6' may be fed, for example, to the sweep circuit ofthe cathode-ray tube, not shown, in order synchronously to trigger thesame. The anode or plate 29 of the cathode-follower tube 21 is showndecoupled to ground through a capacitor 31 and connected through ananode load 33 to the source of positive potential D+.

Connected between the point P and ground is a grid resistor 35 and ashunt or parallel-connected diode D The diode D insures that theelectrical connection from the secondary electron-emitting electrode 13of the tube 1 through the coupling capacitance C to the two loadcircuits represented by the grid of cathode-ray tube and the sweepcircuit, respectively, does not assume an undesirable negativepotential, by providing a shunt connection to ground in the event thatsuch a potential should start to develop. It is also necessary, however,to insure that the grid of the cathode-ray tube is not driven toopositive through the advent of an output pulse from the blockingoscillator of excessive magnitude. To prevent this result, the terminalP is also connected to the anode 24 of a further preferably triodeelectron tube 26, the control-grid electrode 28 of which is returned tothe point P through a resistor 30. The cathode 32 of the tube 26 isconnected to a source of positive potential E+ by a conductor 34, thevalue of E+ being selected to correspond to the predetermined maximumimpulse voltage that it is desired to feed to the cathode-ray tube. Adecoupling capacitor 36 is shown connected from the cathode 32 toground. When, accordingly, the potential at the point P reaches thevalue of the predetermined voltage E+, the tube 26 will conduct and thusprevent the signal being fed out through coupling capacitor C" fromexceeding the desired predetermined value.

Since different-length sweep voltages may be required, the switch S maycommunicate with any of the capacitors C C C C C and C of differentvalues, as desired, thereby correspondingly to vary the duration of theresulting blocking-oscillator output pulse coupled out by the secondaryelectron-emitting electrode 13, as before described. Other types of loadcircuits besides cathoderay tubes may, of course, obviously be employed,also.

Further modifications will occur to those skilled in the art and allsuch are considered to fall within the spirit and scope of theinvention, as defined in the appended claims.

What is claimed is:

l. A blocking oscillator system comprising:

an electron tube provided with input and output circuits, said tubehaving at least cathode, control and anode electrodes and asecondary-electron-emitting electrode;

means for biasing the tube to render the same normally conducting withall voltages and currents substantiah ly stabilized, said biasing meansincluding a biasing potential applied to the cathode;

means for applying a trigger pulse to the input circuit to increaseconduction in the tube thereby initiating the generation of a blockingoscillator impulse;

a feed-back network from the anode to the cathode for feeding back asignal to further increase conduction after the tube has been triggered;and

impedance means connected to the cathode and having a greater effectivevalue when the cathode is under the control of the said cathode biasingpotential than when it is under the control of the feed back signal fromthe anode;

said output circuit being connected to the secondaryelectron-emittingelectrode for coupling out therefrom the blocking oscillator impulse.

2. A blocking oscillator system as claimed in claim 1 and in which thesaid input circuit is connected to said control electrode.

3. A blocking oscillator system as claimed in claim 2 and in which thesaid feed-back network is a capacitanceresistance network.

4. A blocking oscillator system as claimed in claim 3 and in which saidresistancecap-acitance network is provided with a plurality ofcapacitance elements of ditferent values and a switch for selectingcapacitance from said plurality and connecting the same into saidnetwork, the capacitance selected combining with the other elements ofthe network to control the time duration of the blocking oscillatorimpulse.

5. A blocking oscillator as claimed in claim 3 and in which the saidimpedance means comprises a diode and a resistor connected in parallel,said diode oriented in opposition to said cathode biasing potential butpasses said feed-back signal when the biasing potential is overcome.

6. A blocking oscillator system as claimed in claim 5 and in which meansare provided for controlling the polarity and maximum magnitude of theblocking oscillator impulse coupled out from said secondary-electronemitting electrode.

References Cited in the file of this patent UNITED STATES PATENTS1,790,197 Brown Jan. 27, 1931 2,235,190 Alma Mar. 18, 1941 2,297,522Zanarini Sept. 29, 1942 (Other references on following page} 5 UNITEDSTATES PATENTS Miller Dec. 11, 1945 Barnard et a1 Mar. 25, 1947 LevyApr. 27, 1948 Van der Mark et a1 May 30, 1950 5 Toporeck Jan. 23, 1951Glenn July 10, 1951 Wrenn Aug. 14, 1956 Purinton Aug. 5, 1958 OTHERREFERENCES Millrnan and Taub-Pulse and Digital Circuits, Mc- Knaus-sJuly 7, 1959 10 GraW-Hill Boo-k C0., Inc., 1956, page 128.

